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Editors Note: The original patch was modified to use SDL_Delay() instead of nanosleep because nanosleep may not be portable to all systems using SDL with the ALSA backend. This may be a moot point with the switch to blocking writes anyway... Date: Sat, 27 Dec 2003 21:47:36 +0100 From: Michel Daenzer To: Debian Bug Tracking System Subject: [SDL] Bug#225252: [PATCH] ALSA fixes Package: libsdl1.2debian-all Version: 1.2.6-2 Severity: normal Tags: patch For SDL 1.2.6, the ALSA backend was changed to call snd_pcm_open() with SND_PCM_NONBLOCK. That's a good idea per se, however, it causes high CPU usage, interrupted sound and stuttering in some games here. Taking a nanosleep whenever snd_pcm_writei() returns -EAGAIN fixes this, but I think it's more efficient to use blocking mode for the actual sound playback. Feedback from the SDL and ALSA lists appreciated. The patch also fixes the default ALSA device to be used.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 04 Jan 2004 15:40:50 +0000
parents 55f1f1b3e27d
children
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<HTML
><HEAD
><TITLE
>Video Examples</TITLE
><META
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>SDL Library Documentation</TH
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><TD
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><A
HREF="guideexamples.html"
>Prev</A
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><TD
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>Chapter 4. Examples</TD
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>Next</A
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><HR
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="GUIDEVIDEOEXAMPLES"
>Video Examples</A
></H1
><P
></P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN375"
>Initializing the video display</A
></H2
><P
><PRE
CLASS="PROGRAMLISTING"
>    SDL_Surface *screen;

    /* Initialize the SDL library */
    if( SDL_Init(SDL_INIT_VIDEO) &#60; 0 ) {
        fprintf(stderr,
                "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

    /* Clean up on exit */
    atexit(SDL_Quit);

    /* Initialize the display in a 640x480 8-bit palettized mode */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN379"
>Initializing the best video mode</A
></H2
><P
><PRE
CLASS="PROGRAMLISTING"
>    /* Have a preference for 8-bit, but accept any depth */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }
    printf("Set 640x480 at %d bits-per-pixel mode\n",
           screen-&#62;format-&#62;BitsPerPixel);</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN383"
>Loading and displaying a BMP file</A
></H2
><P
><PRE
CLASS="PROGRAMLISTING"
>    SDL_Surface *image;
    SDL_Rect dest;
    int ncolors, i;
    SDL_Color *colors;

    /* Load the BMP file into a surface */
    image = SDL_LoadBMP("sample.bmp");
    if ( image == NULL ) {
        fprintf(stderr, "Couldn't load sample.bmp: %s\n",
                        SDL_GetError());
        return;
    }

    /* Set the display colors -- SDL_SetColors() only does something on
       palettized displays, but it doesn't hurt anything on HiColor or
       TrueColor displays.
       If the display colors have already been set, this step can be
       skipped, and the library will automatically map the image to
       the current display colors.
    */
    if ( image-&#62;format-&#62;palette ) {
        ncolors = image-&#62;format-&#62;palette-&#62;ncolors;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));
        memcpy(colors, image-&#62;format-&#62;palette-&#62;colors, ncolors);
    } 
    else {
        int r, g, b;

        /* Allocate 256 color palette */
        ncolors = 256;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));

        /* Set a 3,3,2 color cube */
        for ( r=0; r&#60;8; ++r ) {
            for ( g=0; g&#60;8; ++g ) {
                for ( b=0; b&#60;4; ++b ) {
                    i = ((r&#60;&#60;5)|(g&#60;&#60;2)|b);
                    colors[i].r = r&#60;&#60;5;
                    colors[i].g = g&#60;&#60;5;
                    colors[i].b = b&#60;&#60;6;
                }
            }
        }
        /* Note: A better way of allocating the palette might be
           to calculate the frequency of colors in the image
           and create a palette based on that information.
        */
    }
    /* Set colormap, try for all the colors, but don't worry about it */
    SDL_SetColors(screen, colors, 0, ncolors);
    free(colors);

    /* Blit onto the screen surface */
    dest.x = 0;
    dest.y = 0;
    dest.w = image-&#62;w;
    dest.h = image-&#62;h;
    SDL_BlitSurface(image, NULL, screen, &#38;dest);

    SDL_UpdateRects(screen, 1, &#38;dest);

    /* Free the allocated BMP surface */
    SDL_FreeSurface(image);
    return;</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN387"
>Drawing directly to the display</A
></H2
><P
><PRE
CLASS="PROGRAMLISTING"
>    /* Code to set a yellow pixel at the center of the screen */

    Sint32   X, Y;
    Uint32   pixel;
    Uint8   *bits, bpp;

    /* Map the color yellow to this display (R=0xFF, G=0xFF, B=0x00)
       Note:  If the display is palettized, you must set the palette first.
    */
    pixel = SDL_MapRGB(screen-&#62;format, 0xFF, 0xFF, 0x00);

    /* Calculate the framebuffer offset of the center of the screen */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) &#60; 0 )
            return;
    }
    bpp = screen-&#62;format-&#62;BytesPerPixel;
    X = screen-&#62;w/2;
    Y = screen-&#62;h/2;
    bits = ((Uint8 *)screen-&#62;pixels)+Y*screen-&#62;pitch+X*bpp;

    /* Set the pixel */
    switch(bpp) {
        case 1:
            *((Uint8 *)(bits)) = (Uint8)pixel;
            break;
        case 2:
            *((Uint16 *)(bits)) = (Uint16)pixel;
            break;
        case 3: { /* Format/endian independent */
            Uint8 r, g, b;

            r = (pixel&#62;&#62;screen-&#62;format-&#62;Rshift)&#38;0xFF;
            g = (pixel&#62;&#62;screen-&#62;format-&#62;Gshift)&#38;0xFF;
            b = (pixel&#62;&#62;screen-&#62;format-&#62;Bshift)&#38;0xFF;
            *((bits)+screen-&#62;format-&#62;Rshift/8) = r; 
            *((bits)+screen-&#62;format-&#62;Gshift/8) = g;
            *((bits)+screen-&#62;format-&#62;Bshift/8) = b;
            }
            break;
        case 4:
            *((Uint32 *)(bits)) = (Uint32)pixel;
            break;
    }

    /* Update the display */
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }
    SDL_UpdateRect(screen, X, Y, 1, 1);

    return;</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN391"
>Fastest possible surface blit</A
></H2
><P
>There are three different ways you can draw an image to the screen: 
<P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
>1.Create a surface and use <A
HREF="sdlblitsurface.html"
><TT
CLASS="FUNCTION"
>SDL_BlitSurface</TT
></A
> to blit it to the screen</TD
></TR
><TR
><TD
>2.Create the video surface in system memory and call <A
HREF="sdlupdaterect.html"
><TT
CLASS="FUNCTION"
>SDL_UpdateRect</TT
></A
></TD
></TR
><TR
><TD
>3.Create the video surface in video memory and call <A
HREF="sdllocksurface.html"
><TT
CLASS="FUNCTION"
>SDL_LockSurface</TT
></A
></TD
></TR
></TBODY
></TABLE
><P
></P
>
The best way to do this is to combine methods: 
<PRE
CLASS="PROGRAMLISTING"
>#include &#60;stdio.h&#62;
#include &#60;stdlib.h&#62;
#include "SDL.h"
#include "SDL_timer.h"

void ComplainAndExit(void)
{
    fprintf(stderr, "Problem: %s\n", SDL_GetError());
    exit(1);
}

int main(int argc, char *argv[])
{
    SDL_PixelFormat fmt;
    SDL_Surface *screen, *locked;
    SDL_Surface *imagebmp, *image;
    SDL_Rect dstrect;
    int i;
    Uint8 *buffer;

    /* Initialize SDL */
    if ( SDL_Init(SDL_INIT_VIDEO) &#60; 0 ) {
        ComplainAndExit();
    }
    atexit(SDL_Quit);

    /* Load a BMP image into a surface */
    imagebmp = SDL_LoadBMP("image.bmp");
    if ( imagebmp == NULL ) {
        ComplainAndExit();
    }

    /* Set the video mode (640x480 at native depth) */
    screen = SDL_SetVideoMode(640, 480, 0, SDL_HWSURFACE|SDL_FULLSCREEN);
    if ( screen == NULL ) {
        ComplainAndExit();
    }

    /* Set the video colormap */
    if ( imagebmp-&#62;format-&#62;palette != NULL ) {
        SDL_SetColors(screen,
                      imagebmp-&#62;format-&#62;palette-&#62;colors, 0,
                      imagebmp-&#62;format-&#62;palette-&#62;ncolors);
    }

    /* Convert the image to the video format (maps colors) */
    image = SDL_DisplayFormat(imagebmp);
    SDL_FreeSurface(imagebmp);
    if ( image == NULL ) {
        ComplainAndExit();
    }

    /* Draw bands of color on the raw surface */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) &#60; 0 )
            ComplainAndExit();
    }
    buffer=(Uint8 *)screen-&#62;pixels;
    for ( i=0; i&#60;screen-&#62;h; ++i ) {
        memset(buffer,(i*255)/screen-&#62;h,
               screen-&#62;w*screen-&#62;format-&#62;BytesPerPixel);
               buffer += screen-&#62;pitch;
    }
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }

    /* Blit the image to the center of the screen */
    dstrect.x = (screen-&#62;w-image-&#62;w)/2;
    dstrect.y = (screen-&#62;h-image-&#62;h)/2;
    dstrect.w = image-&#62;w;
    dstrect.h = image-&#62;h;
    if ( SDL_BlitSurface(image, NULL, screen, &#38;dstrect) &#60; 0 ) {
        SDL_FreeSurface(image);
        ComplainAndExit();
    }
    SDL_FreeSurface(image);

    /* Update the screen */
    SDL_UpdateRects(screen, 1, &#38;dstrect);

    SDL_Delay(5000);        /* Wait 5 seconds */
    exit(0);
}</PRE
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